MongoIdModule

MongoId.java

package com.example.db.mongo;

import java.lang.annotation.Retention;

import static java.lang.annotation.RetentionPolicy.RUNTIME;

@Retention(RUNTIME)

// Override the serializer for ObjectId annotation
public @interface MongoId {
}

MongoIdFieldSelector.java

package com.example.db.mongo;

import java.lang.reflect.Field;

import org.jongo.marshall.jackson.JacksonIdFieldSelector;

/**
 * Extend JacksonIdFieldSelector to look for MongoId objects so that
 * updating the ID of the object after saving it works
 *
 * @see org.jongo.marshall.jackson.JacksonMapper.Builder#withObjectIdUpdater(org.jongo.ObjectIdUpdater)
 */
public class MongoIdFieldSelector extends JacksonIdFieldSelector {

    @Override
    public boolean isId(Field f) {
        return hasIdAnnotation(f) || super.isId(f);
    }

    private boolean hasIdAnnotation(Field f) {
        return f.getAnnotation(MongoId.class) != null;
    }
}

MongoIdModule.java

package com.example.db.mongo;

import java.util.List;

import org.jongo.ReflectiveObjectIdUpdater;
import org.jongo.marshall.jackson.JacksonMapper;
import org.jongo.marshall.jackson.configuration.MapperModifier;
import org.jongo.marshall.jackson.oid.ObjectIdDeserializer;

import com.fasterxml.jackson.databind.BeanDescription;
import com.fasterxml.jackson.databind.DeserializationConfig;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationConfig;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.deser.BeanDeserializerModifier;
import com.fasterxml.jackson.databind.introspect.AnnotatedField;
import com.fasterxml.jackson.databind.introspect.BeanPropertyDefinition;
import com.fasterxml.jackson.databind.module.SimpleModule;
import com.fasterxml.jackson.databind.ser.BeanPropertyWriter;
import com.fasterxml.jackson.databind.ser.BeanSerializerModifier;
import com.fasterxml.jackson.databind.util.NameTransformer;

/**
 * Module to convert to and from
 */
public class MongoIdModule extends SimpleModule {

    @Override
    public void setupModule(SetupContext context) {
        context.addBeanSerializerModifier(new SerializerModifier());
        context.addBeanDeserializerModifier(new DeserializerModifier());
    }

    public static class SerializerModifier extends BeanSerializerModifier {

        @Override
        public List<BeanPropertyWriter> changeProperties(SerializationConfig config, BeanDescription beanDesc, List<BeanPropertyWriter> beanProperties) {
            for (int i = 0; i < beanProperties.size(); i++) {
                BeanPropertyWriter beanPropertyWriter = beanProperties.get(i);
                MongoId annotation = beanPropertyWriter.getAnnotation(MongoId.class);
                if (annotation != null) {
                    BeanPropertyWriter beanPropertyWriterRenamed = beanPropertyWriter.rename(new ToIdTransformer(beanPropertyWriter.getName()));
                    if (beanPropertyWriter.getPropertyType().equals(String.class)) {
                        beanPropertyWriterRenamed.assignSerializer(new MongoIdSerializer());
                    }
                    beanProperties.set(i, beanPropertyWriterRenamed);
                }
            }
            return beanProperties;
        }
    }

    public static class DeserializerModifier extends BeanDeserializerModifier {

        JsonDeserialize deserializeAnnotation;

        @JsonDeserialize(using = ObjectIdDeserializer.class)
        private static class DeserializeUsingObjectId {}

        public DeserializerModifier() {
            deserializeAnnotation = DeserializeUsingObjectId.class.getAnnotation(JsonDeserialize.class);
        }

        @Override
        public List<BeanPropertyDefinition> updateProperties(DeserializationConfig config, BeanDescription beanDesc, List<BeanPropertyDefinition> propDefs) {
            for (int i = 0; i < propDefs.size(); i++) {
                BeanPropertyDefinition propertyDefinition = propDefs.get(i);

                AnnotatedField field = propertyDefinition.getField();
                if (field != null && field.hasAnnotation(MongoId.class)) {
                    field.addIfNotPresent(deserializeAnnotation);
                    propDefs.set(i, propertyDefinition.withName("_id"));
                }
            }
            return propDefs;
        }

    }

    public static class ToIdTransformer extends NameTransformer {

        private static final String ID_FIELD = "_id";

        private String originalName;

        public ToIdTransformer(String originalName) {
            this.originalName = originalName;
        }

        @Override
        public String reverse(String transformed) {
            return originalName;
        }

        @Override
        public String transform(String name) {
            return ID_FIELD;
        }

    }

    public static class MapperModder implements MapperModifier {
        @Override
        public void modify(ObjectMapper mapper) {
            mapper.registerModule(new MongoIdModule());
        }
    }
    
    /**
     * Use this for JacksonMapper setup
     */
    public static JacksonMapper.Builder getMapperBuilder() {
        return new JacksonMapper.Builder()
            .addModifier(new MongoModule.MapperModder())
            .withObjectIdUpdater(new ReflectiveObjectIdUpdater(new MongoIdFieldSelector()));
    }
}

MongoIdSerializer.java

package com.example.db.mongo;

import java.io.IOException;

import org.jongo.marshall.jackson.oid.ObjectIdSerializer;

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;

/**
 * Wrapper for ObjectIdSerializer so that it can be applied on generic objects
 */
public class MongoIdSerializer extends JsonSerializer<Object> {

    private static ObjectIdSerializer objectIdSerializer = new ObjectIdSerializer();

    @Override
    public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
        objectIdSerializer.serialize((String) value, jgen, provider);
    }
}